Metastatic breast cancer, a term for advanced breast cancer that’s spread to other parts of the body, is a devastating diagnosis: Its average life expectancy is just three years, and its five-year survival rate is just 22%. Tumors can be treated and symptoms can be managed, but most patients fight the disease for the rest of their lives. It’s extremely rare, if not unheard of, for someone to be cured altogether.

But this week, doctors at the National Cancer Institute (NCI) revealed that a new type of treatment may have done just that. In a letter published in Nature Medicine, they describe how an ongoing clinical trial has led to the complete regression of metastatic breast cancer in a patient who’d been unresponsive to traditional treatments. Nearly two years later, that patient is still cancer-free.

The promising news is the result of immunotherapy—a type of cancer treatment that stimulates the body’s own immune system to recognize and kill cancer cells. Immunotherapy has been a cancer buzzword for a few years now, and it’s shown surprising success against hard-to-beat cancers like metastatic melanoma and non-Hodgkin lymphoma.

This is the first time, however, that immunotherapy has helped a patient with metastatic breast cancer. NCI investigators say that’s because their new approach is more effective at targeting mutations specific to this type of cancer. Six other patients in the trial (out of 45 total, with various types of cancer) also saw their diseases go into remission after participating in the trial.

So how exactly does this approach work? In the trial, NCI researchers analyzed DNA from each patient’s cancer tumors. They also analyzed patients’ healthy tissue, to see which mutations were unique to their cancers. Then they tested the patients’ immune-system cells—known as T cells—and picked out those that seemed to recognize one or more cancer mutations.

Those specific T cells were extracted and grown to large numbers (tens of billions) in a laboratory, then infused back into the patients—creating a stronger, more targeted immune response. And for some of the patients, it worked: Their newly bolstered immune system was able to kill their tumors, even when chemotherapy and radiation had failed.

Judy Perkins, a 52-year-old retired engineer from Port St. Lucie, Florida, is one of those patients. When she was diagnosed with metastatic breast cancer in 2013, she was told she only had three years to live.

She tried chemotherapy and a slew of experimental treatments, but her tumors kept growing—some as large as tennis balls, Perkins told the BBC. But within a week after her first immunotherapy treatment, those tumors began shrinking. During her first medical scan after the procedure, she said, the staff “were all very excited and jumping around.”

Experts say Perkins’ story is a hopeful sign that this type of personalized treatment may be able to help other patients with metastatic breast cancer, and other types of cancer, as well. But the therapy isn’t available or ready for widespread use just yet: More research is needed for doctors to understand why it works for some people and not for others.

“This research is experimental right now,” said Steven A. Rosenberg, MD, chief of the surgery branch at NCI’s Center for Cancer Research, in a statement. “But because this new approach to immunotherapy is dependent on mutations, not on cancer type, it is in a sense a blueprint we can use for the treatment of many types of cancer.”

Laszlo Radvanyi, president and scientific director of the Ontario Institute for Cancer Research, called Perkins’ case “remarkable” in an article accompanying the new paper. The NCI’s new approach may be “at the cusp of major revolution” in immunotherapy, he wrote, and may help researchers realize “the elusive goal” of targeting different types of cancer mutations.

Perkins tells Health she is grateful to be alive. She hopes that her case report leads to more successful treatments for cancer—and that her story inspires others who are, like she was five years ago, ready to give up.

“Many of the existing therapies that are out there now were once in clinical trials—so there is magic out there, even as we speak, for some people,” she says. “If you are considering a clinical trial, you need to get to a cancer center that has access to clinical trials.”

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There are, of course, risks involved with clinical trials, and not everyone “finds the magic,” Perkins adds. She knows several people who suffered and died, despite getting the same treatment she did. “However, if you have metastatic cancer and you are reaching the end,” she says, “sometimes there isn’t a lot to lose.”